This invention relates to extrusion apparatus for manufacturing extrudable honeycomb structures from materials such as ceramic batches, molten glasses, plastics, molten metals, and similar materials, which have the property of being able to flow or plastically deform during extrusion while being able to become sufficiently rigid immediately thereafter so as to maintain their structural integrity. More particularly, the present invention relates to an improved extrusion die and mask assembly which minimizes the distortion of peripheral cells of the extruded honeycomb structure during the formation of the skin or sheath thereof.
In U.S. Pat. Nos. 3,836,302 to Kaukeinen; 3,947,214 to Cunningham and 4,008,033 to Folmar and Van Dewoestine, various techniques are disclosed for forming extruded honeycomb structures having improved integral skins or sheaths thereabout. In all of these patents, a die body having a plurality of feed passageways which direct extrudate to a larger plurality of discharge slots is placed in conjunction with an extrusion mask which prevents extrusion through at least some of the feed passageways and which partially blocks extrusion through other of the passageways thus compacting extrudate and metering it to form the skin of the finished structure. In the aforementioned Kaukeinen patent, an extrusion mask is diclosed having a central orifice with a tapered side wall which collapses the peripheral cells of the honeycomb structure near the outer surface thereof to simultaneously form an integral skin or sheath about the honeycomb structure. Both the aforementioned Cunningham and Folmar et al patents are improvements over the Kaukeinen patent inasmuch as the number of peripheral cells which are distorted or crushed during extrusion is reduced. In the extrusion masks disclosed by Cunningham and Folmar et al, a peripheral recess is provided about the circumference of the extrusion die mask orifice which meters extrudable material to form the outer skin or sheath of the extruded honeycomb structure.